Observations

Description

Valves are broadly semi-elliptical to semi-circular, with a smoothly arched dorsal margins and convex ventral margins. Valve ends are protracted and capitate. The raphe is located near the ventral margin, straight, with proximal ends straight to slightly dorsally deflected. The axial area is narrow at the poles, widening to form a lanceolate central area. A dorsal fascia is absent. A ventral fascia is present, extending to the ventral margin. Dorsal striae are composed of a single row of areolae, parallel near the central area becoming radiate towards the poles. Ventral striae are radiate near the central area, becoming slightly convergent near the poles.

The systematic position of Halamphora thumensis was under some debate. See Kingston et al. (1980), Krammer (1980) and Levkov (2009) for a thorough discussion.

Valves are small, 9-13 µm in length and broadly semi-elliptical to semi-circular. Valve apices are protracted and capitate. The raphe is straight. The axial area is narrow at the poles, widening to form a lanceolate central area. Dorsal striae are composed of a single areola.

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Due to its small size and unique shape, Halamphora thumensis is easily distinguished from other North American Halamphora taxa.